MerCruiser 305 CID (5.0L) Service Manual page 657

DIAGNOSTICS
Chart A-3 (1 of 2): Engine Cranks But Will Not Run
TO INJECTOR FUSE
439 PNK/BLK
OR PNK
CIRCUIT DESCRIPTION:
In the Distributor Ignition (Dl) system and the fuel injector circuit, the supply voltage comes
from the EFI system relay. From the EFI system relay, CKT 902 delivers supply voltage to
the injector/ECM fuse, and to the ignition coil.
After supply voltage passes through the injector/ECM fuse, it branches out into two separate
CKT's 439. The ECM will control the opening and closing of the injectors through injector
driver CKT 467 and CKT 468 by connecting them to ground.
DIAGNOSTIC AIDS:
This chart assumes that battery voltage and engine cranking speed are OK, and there is
adequate fuel in the tank.
Water or foreign material in fuel system can cause a no start.
A defective MAP sensor may cause a no start or a start and stall condition. To determine
if the MAP sensor is causing the problem, disconnect the electrical connector. The ECM will
then use a default value for the sensor. If the condition is corrected and the connections are
OK, then replace the sensor.
An intermittent may be caused by a poor connection, rubbed through wire insulation or a
wire broken inside the insulation. Check for the following items:
Poor connection or damaged harness. Inspect the ECM harness and connectors for
improper mating, broken locks, improperly formed or damaged terminals, poor terminal to
wire connection, and damaged harness.
If above are all OK, refer to "Hard Start" in "Troubleshooting" section.
Index
Page 5G-30
INJECTORS - ONE IF EFI, FOUR IF MPI
(INJECTORS 2, 3, 5, 8 - IF FOUR)
INJECTORS - ONE IF EFI, FOUR IF MPI
(INJECTORS 1, 4, 6, 7 - IF FOUR)
SERVICE MANUAL NUMBER 24
MEFI 1
MEFI 2
467 DK BLU
J2-21
J2-5
468 DK GRN
90-861327--1 OCTOBER 1999
ECM
MEFI 3
J1-1
J1-17